Abrasive machine and method of abrading work piece

ABSTRACT

The abrasive machine of the present invention is capable of changing pressure applied to a work piece and easily defining optimum abrading conditions.  
     The abrasive machine comprises: a pressure vessel capable of increasing and reducing inner pressure; an abrasive plate provided in the pressure vessel; a pressing plate provided on the abrasive plate, the pressing plate pressing the work piece onto the abrasive plate; a driving unit relatively moving the abrasive plate with respect to the pressing plate so as to abrade the work piece; and a pressure source connected to the pressure vessel, the pressure source increasing or reducing the inner pressure of the pressure vessel.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an abrasive machine and a methodof abrading a work piece, e.g., silicon wafer.

[0002] A technique of Chemical-Mechanical Polishing (CMP) is consideredas an important technique for high density multi-layered wiring.

[0003] There are many related factors in the CMP, such as kinds ofslurry, rotational speed of an abrasive plate, kinds of abrasive pads,temperature, etc. Therefore it is difficult to select optimum abradingconditions under which desired abrasion rate and flatness can be gained.

SUMMARY OF THE INVENTION

[0004] The present invention has been invented so as to overcome thedisadvantage of the CMP.

[0005] An object of the present invention is to provide an abrasivemachine and a method of abrading a work piece capable of changingpressure applied to the work piece, which seldom relates to the CMPfactors, and easily defining the optimum abrading conditions.

[0006] To achieve the object, the present invention has followingstructures.

[0007] Namely, the abrasive machine of the present invention comprises:

[0008] a pressure vessel having a lid which opens or closes the pressurevessel, the pressure vessel being capable of increasing and reducinginner pressure;

[0009] an abrasive plate being provided in the pressure vessel;

[0010] a pressing plate being provided on the abrasive plate, thepressing plate pressing a work piece, which has been set between theabrasive plate and the pressing plate, onto the abrasive plate;

[0011] a driving unit relatively moving the abrasive plate with respectto the pressing plate so as to abrade the work piece; and

[0012] a pressure source being connected to the pressure vessel, thepressure source increasing or reducing the inner pressure of thepressure vessel.

[0013] On the other hand, the method of the present invention is amethod of abrading a work piece in an abrasive machine comprising: apressure vessel having a lid which opens or closes the pressure vessel,the pressure vessel being capable of increasing and reducing innerpressure; an abrasive plate being provided in the pressure vessel; apressing plate being provided on the abrasive plate, the pressing platepressing a work piece, which has been set between the abrasive plate andthe pressing plate, onto the abrasive plate; a driving unit relativelymoving the abrasive plate with respect to the pressing plate so as toabrade the work piece; and a pressure source being connected to thepressure vessel, the pressure source increasing or reducing the innerpressure of the pressure vessel,

[0014] the method comprises the steps of:

[0015] setting the work piece between the abrasive plate and thepressing plate;

[0016] introducing a gas into the pressure vessel; and

[0017] relatively moving the abrasive plate with respect to the pressingplate by the driving unit so as to abrade the work piece.

[0018] In the present invention, the abrasive plate and the pressingplate are provided in the pressure vessel, and the work piece can beabraded in a state-of increasing or reducing the inner pressure of thepressure vessel, so that the abrading conditions can be easilycontrolled by adjusting the inner pressure of the pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the present invention will now be described by wayof examples and with reference to the accompanying drawings, in which:

[0020]FIG. 1 is a front sectional view of an abrasive machine of anembodiment of the present invention;

[0021]FIG. 2 is a plan view of the abrasive machine, in which a lid isopened;

[0022]FIG. 3 is a plan view of a bell jar;

[0023]FIG. 4 is an explanation view a pressure source connected to thebell jar;

[0024]FIG. 5 is an explanation view of a driving unit of anotherexample;

[0025]FIG. 6 is an explanation view of the driving unit of otherexample;

[0026]FIG. 7 is an explanation view of a mechanism for moving anabrasive plate;

[0027]FIG. 8 is a sectional view of a press-type pressing plate;

[0028]FIG. 9 is a graph showing a relationship between air pressure andabrasion rate;

[0029]FIG. 10 is a graph showing a relationship between oxygen gaspressure and abrasion rate;

[0030]FIG. 11 is a graph showing a relationship between nitrogen gaspressure and abrasion rate;

[0031]FIG. 12 is a graph showing a relationship between argon gaspressure and abrasion rate;

[0032]FIG. 13 is a graph of rate of abrading a copper layer in variousgas atmospheres;

[0033]FIG. 14 is a graph of rate of abrading an Si substrate in thevarious gas atmospheres;

[0034]FIG. 15 is a graph of rate of abrading an SiO₂ layer in thevarious gas atmospheres;

[0035]FIG. 16 is a sectional view of copper wires implanted in a barriermetal layer; and

[0036]FIG. 17 is a sectional view of the implanted copper wires exposed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Preferred embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings.

[0038]FIG. 1 is a front sectional view of an abrasive machine of anembodiment of the present invention;

[0039]FIG. 2 is a plan view of the abrasive machine, in which a lid isopened; and FIG. 3 is a plan view of a bell jar.

[0040] The bell jar 12 has a lid 14 and acts as a pressure vesselcapable of bearing increase and reduce of pressure therein. The lid 14is pivotably attached to a body proper 16 of the bell jar 14 by a shaft15 so as to open and close the body proper 16.

[0041] A lower end of a clamping bolt 18 is pivotably attached to thebody proper 16 by a shaft 21; an upper end of the bolt 18 is capable ofentering a gap between U-shaped forks of a fixed arm 19. By turning anut 20, the lid 14 can air-tightly close the body proper 16. In thepresent embodiment, six clamping bolts 18 are provided with angularseparations of 60 degrees.

[0042] The body proper 16 is made of steel having a prescribed thicknessand formed into a bottomed cylindrical shape. A top plate of the lid 14is curved upward. With this pressure-resisting structure, the bell jar12 can act as the pressure vessel. A bottom section 16 a of the bodyproper 16 is a flat plate, and its thickness is much thicker than thatof a cylindrical section so as to bear inner pressure.

[0043] Note that, the shape of the bell jar 12 is not limited to thecylindrical shape. Other pressure vessels which have enoughpressure-resisting structure can be employed in the present invention.

[0044] An abrasive plate 23 is provided in the bell jar 12.

[0045] An abrasive cloth or an abrasive pad (not shown), which is madeof a known material, is adhered on an upper face of the abrasive plate23.

[0046] A connecting member 24, which is formed into a cylindrical shape,is fixed on a bottom face of the abrasive plate 23. The connectingmember 24 is connected to a rotary shaft 26, which is rotatably held bya bearing 25 of the bottom section 16 a, by a key 27. With thisstructure, the abrasive plate 23 is rotated together with the rotaryshaft 26. A symbol 28 stands for a sealing member.

[0047] A lower end part of the abrasive plate 23 is supported by athrust bearing 29. A supporting member 30 is provided on the bottomsection 16 a, and the thrust bearing 29 is provided on the supportingmember 30.

[0048] A cover 31 encloses an outer circumferential face of the abrasiveplate 23 so as to remain prescribed amount of slurry on the abrasiveplate 23. Note that, the cover 31 may be omitted.

[0049] A supporting base 32 supports the bell jar 12 and has four legs32 a. An adjustable bolt 33 is provided to a lower end of each leg 32 aso as to adjust height of the supporting base 32 and levelness of thebell jar 12.

[0050] A motor 35, which acts as a driving unit, is attached to thesupporting base 32. A motor shaft of the motor 35 is connected to therotary shaft 26, so that the motor 35 can rotate the abrasive plate 23.In the present embodiment, the motor 35 is provided outside of the belljar 12, but the motor 35 may be provided in the bell jar 12.

[0051] A pressing plate 36 for pressing a work piece (not shown) isprovided on the abrasive plate 23. The pressing plate 36 applies ownweight to the abrasive plate 23 as a pressing force. The work piece tobe abraded is set or sandwiched between the abrasive plate 23 and thepressing plate 36.

[0052] A plurality of weights 37 are mounted on the pressing plate 36 soas to adjust the pressing force. The weights 37 act as a press unit forapplying pressure to the work piece. Note that, number of the weights 37is optionally determined on the basis of abrading conditions.

[0053] A roller 38, which is coaxial with the abrasive plate 23, and aroller, which is provided above an outer edge of the abrasive plate 23,contact an outer edge of the pressing plate 36, so that the pressingplate 36 can be held at a prescribed position on the abrasive plate 23.The rollers 38 and 39 are rotatably held by an arc-shaped arm 40provided in the bell jar 12.

[0054] In FIG. 2, the abrasive plate 23 is rotated in a direction “A”.By rotating the abrasive plate 23, the pressing plate 36 too is rotated,about its own axis, in the same direction.

[0055] Note that, the roller 38 may be rotated by a motor (not shown) soas to rotate the pressing plate 36, which contacts the roller 38, in aprescribed direction.

[0056] A proper amount of slurry is stored in the body proper 16. In thepresent embodiment, a lower part of the body proper 16 acts as a slurrystoring section 16 b (see FIG. 4).

[0057] As shown in FIG. 4, the slurry stored in the body proper 16 iscirculated by a circulation pump 43.

[0058] The circulation pump 43 is connected to a pipe 44, which isconnected to the slurry storing section 16 b, and a pipe 45, which isconnected to an upper part of the body proper 16. The slurry stored inthe slurry storing section 16 b is drawn by the pump 43 and suppliedonto the abrasive plate 23 via the pipe 45. The slurry, which has beenused to abrade the work piece, is collected in the slurry storingsection 16 b.

[0059] The slurry storing section 16 b, the circulation pump 43 and thepipes 44 and 45, etc. constitute a slurry supplying unit. Note that, asymbol 44 a shown in FIG. 1 stands for a connecting section of the pipe44.

[0060] The slurry storing section 16 b, of course, may be providedoutside of the bell jar 12.

[0061] In FIG. 4, a pressurizing unit 47 and a pressure reduction unit48 constitute a pressure source.

[0062] The pressurizing unit 47 is connected to the body proper 16 via apipe 49 so as to introduce a pressurized fluid into the bell jar 12. Inthe present embodiment, air, oxygen, nitrogen and argon gas are employedas the fluid. Other gasses may be optionally employed. The fluids areselected and supplied into the bell jar 12 by a switching valve (notshown). A pressure reduction valve 51 is provided so as to supply thefluid into the bell jar 12 with predetermined pressure. Symbols 52 and53 are valves, and a symbol 54 is a flow control valve capable ofcontrolling amount of flow of the fluid.

[0063] Note that, a mixed gas may be employed as the fluid.

[0064] The pressure reduction unit 48 is connected to a part of the pipe49, which is located between the valves 52 and 53. A symbol 56 standsfor a valve.

[0065] The pressure reduction unit 48 includes a vacuum pump.

[0066] Note that, a symbol 49 a shown in FIG. 1 stands for a connectingsection of the pipe 49.

[0067] By closing the valve 56 and opening the valves 52 and 53, thepressurized fluid can be introduced into the bell jar 12, so that innerpressure of the bell jar 12 can be increased. On the other hand, byclosing the valve 52 and opening the valves 53 and 56, the pressurereduction unit 48 sucks the fluid in the bell jar 12, so that the innerpressure of the bell jar 12 can be reduced.

[0068] A pressure gauge 57, which acts as a measuring equipment,measures the inner pressure of the bell jar 12. Other equipments formeasuring temperature, humidity, etc. may be provided if required.

[0069] A safety valve 58 releases the pressurized fluid outside when theinner pressure of the bell jar 12 exceeds a prescribed value. A symbol60 a stands for a viewing window (see FIG. 3).

[0070] Another example of the driving unit is shown in FIG. 5.

[0071] A motor 64 including a stator 59 and a rotor 63 is provided inthe bell jar 12, and the abrasive plate 23 is fixed on the rotor 63. Amotor driver 65 is provided outside of the bell jar 12, and electricpower is supplied to stator coils via wires 66. Note that, the motor 64is a known electric motor.

[0072] In this driving unit, only the wires 66 should be sealed,therefore the sealing mechanism can be simplified.

[0073] Further, another example of the driving unit is shown in FIG. 6.

[0074] In this example, the abrasive plate 23 is rotated by magneticcoupler means. Namely, a first magnet rotor 67, in which North magneticpoles and South magnetic poles are alternately formed on an outercircumferential face, is rotated by a motor 68. By rotating the firstmagnet rotor 67, a second magnet rotor 69 is rotated. The abrasive plate23 is fixed on the second magnet rotor 69.

[0075] With this structure, the abrasive plate 23 can be rotated withoutcontacting any members located outside, therefore an inner space of thebell jar 12 can be clean.

[0076] In the present embodiment, the abrasive plate 23 is rotated aboutits own axis. In another embodiment, the abrasive plate 23 may be movedin a plane parallel to an abrasive face (the upper face) of the abrasiveplate 23. This embodiment is shown in FIG. 7.

[0077] In FIG. 7, a plurality of crank shafts 70 are attached to theabrasive plate 23, and the crank shafts 70 are synchronously rotated bya driving unit (not shown), which is provided outside of the bell jar12. With this structure, the abrasive plate 23 can be moved along acircular orbit with fixed heading. Namely, all points in the abrasiveplate 23 equally rotate in a direction “B”.

[0078] In the above described embodiment, the work piece is merelypressed onto the abrasive plate 23 by the pressing plate 36. The workpiece may be adhered on a bottom face of the pressing plate 36. In thiscase, the abraded work piece is peeled from the pressing plate 36 whenthe abrasion is completed.

[0079] The pressing member 36 may have sucking means for holding thework piece by producing negative pressure. In this case, the suckingmeans may suck and hold the work piece directly or with an elasticbucking member.

[0080] In the above described embodiment, the weights 37 are employed asthe press unit. A cylinder unit (not shown) provided on the arm 40 maybe employed to apply pressure to the work piece.

[0081] Further, a pressure head-type pressing plate may be employed. Anexample of the pressure head-type pressing plate 36 is shown in FIG. 8.

[0082] A holding member 73 is suspended in a head proper 72 by anelastic ring member 74, e.g., diaphragm. With this structure, a pressurechamber 75 is formed. The pressurized fluid is introduced into thepressure chamber 75, so that the work piece held on a bottom face of theholding member 73 is pressed onto the abrasive plate 23. Preferably, thepressing plate 36 is rotated about a rotary shaft 76 by a motor (notshown). A driving mechanism including the motor may be provided on thearm 40.

[0083] Further, the pressing plate 36 may be vertically moved by acylinder unit (not shown) so as to move to and away from the abrasiveface (the abrasive cloth) of the abrasive plate 23. In this case, therotary shaft 76 may be rotatably held by a holding arm (not shown), andthe holding arm may be vertically moved by a cylinder unit (not shown)provided on the arm 40.

[0084] The driving mechanism allows the rotary shaft 76 to verticallymove in a prescribed range and transmits torque of the motor.

[0085] The pressurized fluid is introduced into the pressure chamber 75via a fluid path 77 formed in the rotary shaft 76. The fluid isintroduced into the fluid path 77 via a rotary joint (not shown).

[0086] A restraining ring 78 prevents the holding member 73 from comingout from the head proper 72 and guides the vertical movement of theholding member 73.

[0087] An O-ring 79 is provided between an inner circumferential face ofthe head proper 72 and an outer circumferential face of the holdingmember 73. The O-ring 79 absorbs horizontal movement of the holdingmember 73 and prohibits the slurry to enter the head proper 72.

[0088] Experiments were executed in the abrasive machine 10 under thefollowing conditions. Note that, the inner air pressure of the bell jar12 was varied; and the copper layer, the SiO₂ layer and the Si substrateof the work piece were abraded.

[0089] The conditions were,

[0090] Abrasive cloth: IC1000/SUBA400 (trade name), diameter 200 mm;

[0091] Slurry:

[0092] silica slurry “SS-25” for SiO₂

[0093] colloidal silica “Compol-80” for Si

[0094] alumina slurry for Copper;

[0095] Pressing force of the pressing plate 36: 100-500 g/cm²;

[0096] Rotational speed of the abrasive plate 23: 15-90 rpm; and

[0097] Abrasion time: 2-4 min.

[0098] The work piece were abraded with the fixed pressing force, thefixed rotational speed and the fixed abrasion time under aboveconditions. The results are shown in FIG. 9.

[0099] In FIG. 9, the inner pressure of zero is the atmosphericpressure. Namely, the horizontal axis or the inner pressure of the belljar 12 indicates the pressure added to and reduced from the atmosphericpressure.

[0100] As clearly shown in FIG. 9, abrasion rate under the atmosphericpressure was minimum; the abrasion rate was increased in nearlyproportion to increasing and reducing the inner pressure.

[0101] Especially, in the case of abrading the SiO₂ layer and the Sisubstrate, the abrasion rate of 200 KPa was about twice as great as thatof the atmospheric pressure; and the abrasion rate of 500 KPa was about2.5 times as great as that of the atmospheric pressure.

[0102] In the case of abrading the copper layer, the minimum abrasionrate appeared on the negative pressure side (about −50 KPa). Namely, theminimum abrasion rate was slightly shifted toward the negative pressureside, but the abrasion rate was increased on the both sides of theminimum as well as the SiO₂ layer and the Si substrate.

[0103] The inventor thinks that the reasons of increasing the abrasionrate under the positive pressure are: the fluid pressure is applied tothe pressing plate 36; and the slurry is permeated into the abrasivecloth by the fluid pressure.

[0104] The reason of increasing the abrasion rate under the negativepressure is not clearly found. The inventor thinks that frictional heatbetween the work piece and the abrasive cloth is hardly radiated due topressure reduction so that temperature rises and reaction rate isincreased. By increasing the reaction rate, the abrasion rate isincreased under the negative pressure.

[0105]FIG. 10 is a graph showing a relationship between oxygen gaspressure and the abrasion rate. Oxygen was used as the fluid instead ofthe air.

[0106] Tendency of the case of employing oxygen is nearly equal to thatof the case employing the air. Especially, in the case of abrading thecopper layer, the abrasion rate was much increased under high pressure.

[0107] According to the results, the abrasion rate can be controlled byadjusting the inner pressure of the bell jar 12 without changing otherconditions.

[0108] For example, when the abrasion is started and the work piece isroughly abraded, the inner pressure of the bell jar 12 is increased orreduced so as to abrade the work piece with high abrasion rate; when thework piece is finished and the work piece, the inner pressure of thebell jar 12 is returned to zero or the atmospheric pressure so as toabrade the work piece with low abrasion rate.

[0109] Of course, the abrasion rate may be controlled by combining otherfactors, e.g., the rotational speed of the abrasive plate 23.

[0110] In the case of using a plurality of kinds of slurry or abrasivecloth, a plurality of abrading stations are provided in one abrasivemachine, so that the abrasive machine must be large. However, the innerpressure of the bell jar 12 and the rotational speed of the abrasiveplate 23 can be changed at one abrading station, so number of theabrading stations can be reduced, the abrading conditions can be easilydetermined, a size of the abrasive machine can be smaller andmanufacturing cost of the machine can be reduced.

[0111] The slurry accommodated in the bell jar 12 is pressurized andcirculated, so load of the circulation pump 43 is not so great.

[0112] If the slurry storing section is provided outside of the bell jar12, the slurry is introduced into the bell jar 12 whose inner pressurehas been increased, so that a high power circulation pump is required.

[0113] The slurry may stay in the bell jar 12. In this case, theabrasive plate 23 is inclined with respect to the horizontal plane, byadjusting the adjustable bolts 33, so as to dip a lower part of thesurface of the abrasive plate 23 in the slurry. With this structure, theslurry can be always permeated into the abrasive cloth for abrading thework piece.

[0114]FIG. 11 is a graph showing a relationship between nitrogen gaspressure and the abrasion rate. An inert gas, e.g., nitrogen, was usedas the fluid instead of the air. The air in the bell jar 12 was purgedby nitrogen, then the inner pressure was increased and reduced.

[0115] Under the negative pressure, the abrasion rate was increased aswell as the case of employing air and oxygen (see FIGS. 9 and 10).

[0116] On the other hand, under the positive pressure, especially in thecase of abrading the copper layer, the abrasion rate was reduced until400 KPa.

[0117] The inventor thinks that the copper layer is easily oxidize,therefore a mechanism of the abrasion under the non-oxygen atmosphere(see FIG. 11) is different from that under the oxygen atmosphere (seeFIGS. 9 and 10). Namely, under the oxygen atmosphere, the copper layeris etched by the slurry and the oxidation, so that the abrasion rate ishigh; under the non-oxygen atmosphere, the copper layer is etched by theslurry only, so that the abrasion rate is low.

[0118]FIG. 12 is a graph showing a relationship between argon gaspressure and the abrasion rate. Argon was used as the fluid.

[0119] As clearly shown in the drawing, tendency of the case ofemploying the argon gas is nearly equal to that of the case employingthe nitrogen gas.

[0120]FIG. 13 is a graph of the rate of abrading the copper layer invarious gas atmospheres.

[0121]FIG. 14 is a graph of the rate of abrading the Si substrate in thevarious gas atmospheres.

[0122]FIG. 15 is a graph of the rate of abrading the SiO₂ layer in thevarious gas atmospheres.

[0123] By properly selecting the pressurized fluid, the abrasion ratecan be controlled by adjusting the fluid pressure only. In the case ofselectively employing the fluids (gasses), a plurality of gas supplyingunits which respectively supply different gasses are provided in oneabrasive machine 10, and the gas supplying units are selected by aswitching valve.

[0124] A method of abrading implanted copper wires, which are insulatedby the SiO₂ layer, will be explained with reference to FIG. 16 as anexample.

[0125] A barrier metal layer 61 prevents the copper from diffusing intothe SiO₂ layer 60. The barrier metal layer 61 is made of tantalumnitride (TaN) or made by spattering tantalum (Ta). The copper layer 62is made by electrolytic plating, etc.

[0126] The copper layer 62 is abraded, for example, in the pressurizedair, with high abrasion rate until the barrier metal layer 61 isexposed.

[0127] A metal constituting the barrier metal layer 61 is harder thancopper, if the abrasion is further continued, the copper layer 62 isabraded more, so that of the implanted wires will be too thin.

[0128] Thus, for example, the copper layer 62 is abraded in thepressurized nitrogen (see FIG. 11) with low abrasion rate; the barriermetal layer 61 is abraded with high abrasion rate. With this manner, thebarrier metal layer 61 and the copper layer 62 can be abraded at thesame abrasion rate, so that proper implanted wires 62 a can be formed asshown in FIG. 17.

[0129] The fluid in the bell jar 12 can be changed in one abrasion cycleso as to change the abrasion rate, so that the abrading conditions canbe easily changed. The rotational speed of the abrasive plate 23, ofcourse, may be controlled simultaneously.

[0130] The invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by he foregoing descriptionand all changes which come within the meaning and range of equivalencyof the claims are therefore intended to be embraced therein.

What is claimed is:
 1. An abrasive machine, comprising: a pressurevessel having a lid which opens or closes said pressure vessel, saidpressure vessel being capable of increasing and reducing inner pressure;an abrasive plate being provided in said pressure vessel; a pressingplate being provided on said abrasive plate, said pressing platepressing a work piece, which has been set between said abrasive plateand said pressing plate, onto said abrasive plate; a driving unitrelatively moving said abrasive plate with respect to said pressingplate so as to abrade the work piece; and a pressure source beingconnected to said pressure vessel, said pressure source increasing orreducing the inner pressure of said pressure vessel.
 2. The abrasivemachine according to claim 1, wherein said driving unit moves saidabrasive plate in a plane parallel to an abrasive face.
 3. The abrasivemachine according to claim 1, wherein said driving unit rotates saidabrasive plate in a plane parallel to an abrasive face.
 4. The abrasivemachine according to claim 1, further comprising a slurry supplying unitsupplying slurry onto said abrasive plate.
 5. The abrasive machineaccording to claim 1, wherein said pressure source has: a plurality ofgas supplying units which respectively supply different gasses so as toincrease the inner pressure; and a switching valve for switching the gassupplying unit to be connected to said pressure vessel.
 6. The abrasivemachine according to claim 1, further comprising an equipment formeasuring the pressure in said pressure vessel.
 7. The abrasive machineaccording to claim 1, wherein said driving unit is provided outside ofsaid pressure vessel.
 8. The abrasive machine according to claim 1,further comprising a plurality of rollers contacting an outer edge ofsaid pressing plate so as to hold said pressing plate at a prescribedposition on said abrasive plate.
 9. The abrasive machine according toclaim 8, wherein said rollers are rotatably held by an arm provided insaid pressure vessel.
 10. The abrasive machine according to claim 1,further comprising a press unit applying pressure to the work piece. 11.The abrasive machine according to claim 1, wherein a plurality of saidpressing plates are provided.
 12. The abrasive machine according toclaim 4, wherein said slurry supplying unit has: a slurry storingsection being provided in said pressure vessel, said slurry storingsection storing the slurry therein; and a circulation pump beingprovided outside of said pressure vessel, said circulation pump beingconnected to said slurry storing section and said pressure vessel so asto circulate the slurry between said slurry storing section and saidabrasive plate.
 13. The abrasive machine according to claim 4, whereinsaid slurry supplying unit has a slurry storing section being providedin said pressure vessel, said slurry storing section storing the slurrytherein, and a surface of said abrasive plate is inclined with respectto a horizontal plane so as to dip a lower part of the surface of saidabrasive plate in the slurry.
 14. A method of abrading a work piece inan abrasive machine comprising: a pressure vessel having a lid whichopens or closes said pressure vessel, said pressure vessel being capableof increasing and reducing inner pressure; an abrasive plate beingprovided in said pressure vessel; a pressing plate being provided onsaid abrasive plate, said pressing plate pressing a work piece, whichhas been set between said abrasive plate and said pressing plate, ontosaid abrasive plate; a driving unit relatively moving said abrasiveplate with respect to said pressing plate so as to abrade the workpiece; and a pressure source being connected to said pressure vessel,said pressure source increasing or reducing the inner pressure of saidpressure vessel, said method comprising the steps of: setting the workpiece between said abrasive plate and said pressing plate; introducing agas into said pressure vessel; and relatively moving said abrasive platewith respect to said pressing plate by said driving unit so as to abradethe work piece.
 15. The method according to claim 14, wherein saidabrasive machine further comprises a slurry supplying unit, and theslurry is supplied from said slurry supplying unit to said abrasiveplate.
 16. The method according to claim 14, wherein inner pressure ofsaid pressure vessel is varied while abrading the work piece.
 17. Themethod according to claim 14, wherein the gas in said pressure vessel isexchanged to another gas while abrading the work piece.
 18. The abrasivemachine according to claim 1, wherein said pressure vessel is a belljar.
 19. The method according to claim 14, wherein said pressure vesselis a bell jar.